Providing a motor system operational in a single plane and capable of fine controllable movement in the XY plane is highly desirable.
This invention relates to motors for effecting movement in an XY plane. In particular, the invention is directed to a system of linear motors operating such that control of movement of a shuttle in the plane can be finely regulated, and wherein the angular movement can be restrained.
Modern technology requires a system where a shuttle can move in a XY plane, and wherein the profile of the motor system and shuttle is maintained relatively low. As such, a workpiece can be located on the shuttle which is located on a table so that it is mounted strategically relative to different tools or other elements. Work can then be conducted on workpieces or components on the table as required.
As components have grown smaller in size, it is necessary to be able to locate tools and the like more precisely relative to the workpiece along XY coordinates. Operations need to be effected on the component within an accuracy of one tenth of a thousandth of an inch of accuracy, or even closer tolerances.
It is known to locate two linear motors orthogonally relative to each other in a piggy-back relationship. U.S. Pat. No. 4,808,892 (Dreibelbis). These motors operate in two different planes, namely a compound or multi-planar relationship. The difficulty with this configuration is the height of the structure. Such multi-plane systems operate with DC motors such that accurate movement in each orthogonal direction can be controlled. The multi-planar configuration, namely the height of the system, however, is a disadvantage in the overall construction of apparatus operating in an XY plane.
It is known to have linear stepper motors operate in a single plane such that a platen, shuttle or the motor itself can move in the XY plane. U.S. Pat. Nos. 3,376,578 and 3,857,078 (Sawyer). As part of this system, linear stepper motors are incorporated in the shuttle which moves over a waffle surface. A disadvantage of such a system is that the waffle surface which is used for interaction with the motor has discrete magnetic elements in the form of pinhead elements arranged on the base about which the platen, shuttle or motor unit moves. The pinhead elements cannot be reduced beyond a predetermined size. The motor movement across the base is thus effected in steps greater than several thousandths of an inch. Such accuracy is not adequate in many applications requiring finer motion control with modern technology applications. As a consequence, such stepper motor operation has its limitations in fine movement control.
The typical pitch of the surface as defined by the pinhead is about 0.04 inch. Each pulse of power causes a stepper linear motor which is part of the shuttle system to move in a microstep manner such that the motion of each step is in the order of 0.01 inch for a two-phase motor or 0.005 inch for a four-phase motor. This is insufficiently fine control for modern technology needs.
This relative inaccuracy is further aggravated in that where there is an open loop system with such linear stepper motors there is the possibility that the motor will go out of synchronization and lose position.
Another manner of regulating movement in a single plane is effected by a DC motor movable over a checkerboard plane of different magnetic fields. Such a system is disclosed in U.S. Pat. No. 4,654,571, by the present applicant (Hinds). Such a system requires complex laser beam and laser interferometer detection means for regulating movement of the shuttle over the plane.
Linear DC motors having feedback means are wellknown. U.S. Pat. Nos. 4,560,911 and 4,761,573 (Chitayat) describe such motors. The feedback means can facilitate very accurate control of movement of a table, platen or the like in a single direction.
It is unknown to provide a system of linear motors whereby a platen, table or shuttle can be moved in more than one direction, namely an XY direction, which is a compound orthogonal direction with the same degree of accuracy as movement of the shuttle in a single direction.
There is a need for having a motor system providing for accurate XY movement, which has a relatively low profile, and which has the ability to be restrained in angular movement.